The University Group Diabetes Program (UGDP) was undertaken for the purpose of evaluating the effect of hypoglycemic treatment on the rate of development of vascular complications in mild adult-onset diabetics. It is a multi-clinic study involving 12 Clinical Centers and a Coordinating Center. Patient recruitment in this study started in February 1961 and was completed in early 1966 after a total of 1,027 patients had been enrolled. Patients were randomly assigned to one of the following treatment groups; insulin given in fixed dose, insulin given in variable dose to maintain blood glucose levels within a normal range, tolbutamide, phenformin or placebo. All patients were placed on diets designed to achieve or to maintain normal body weight. Information obtained from the study is used to evaluate the efficacy of treatments under study in preventing or delaying the onset and development of vascular complications in mild diabetics and to provide detailed information on the natural history of diabetes. This application contains the justification for support for the 12 participating Clinical Centers for one additional year for the purpose of completing data collection under the original study protocol, providing for mortality follow-up and enabling the participation of the clinical investigators in the preparation of first reports.